Find a guide that matches what your vehicle is doing. These 100 focused articles explain useful observations, diagnostic limits and the information to collect before an assessment. A fault code or symptom alone does not prove that a module needs replacement.
For help choosing a route, start with your symptoms or prepare a vehicle and module enquiry. Workshop assessments are in Didcot; contact AXION to confirm suitability and arrangements before travelling or sending a unit.
EV charging
- EV Charges at Work but Not at Home: Comparing Two Sessions
- EV Charges on AC but Refuses DC Rapid Charging
- EV Charges on DC but Refuses AC Charging
- EV Charging Stops at the Same Percentage Each Time
- EV Charging Power Falls During a Session: What the Graph Means
- Charging App Says Complete but the EV Is Not Fully Charged
- EV Charging Fails Only in Wet Weather
- EV Charging Session Restarts Repeatedly Overnight
- EV Charge Inlet Damage: What to Send Before an Assessment
- Public Charger Rejects the Session Before the Car Starts Charging
EV and hybrid thermal systems
- EV Has Cabin Heat but the Demister Is Poor
- EV Heating Works on One Side Only
- EV Heating Stops During a Charging Session
- EV Cooling Fan Runs After Parking: Normal Operation or a Fault?
- EV Cooling-Pump Noise: Describe the Sound and the Conditions
- EV Air Conditioning Fault with a Battery-Temperature Warning
- EV Cabin Preconditioning Fails but Heating Works While Driving
- Hybrid Heater Goes Cold When the Engine Stops
- Climate Display Works but the Cabin Fan Does Not
- Heated Seats Switch Off Immediately: Control, Load or Protection?
Body controls and vehicle access
- One Door Will Not Unlock but the Others Work
- Central Locking Works but the Dashboard Says a Door Is Open
- Remote Key Locks the Car but Will Not Unlock It
- Keyless Entry Fails at One Handle Only
- Tailgate Release Works from the Key but Not the Exterior Switch
- Power Tailgate Reverses Before Closing
- Fuel Filler Flap Will Not Unlock
- Car Alarm Sounds Randomly While Parked
- Interior Lights Stay On After Locking
- Electric Window Works from One Switch but Not the Other
Windows, lighting and body electronics
- Electric Window Reverses Near the Top
- Folding Mirror Stops Halfway
- Heated Rear Window Indicator Is On but the Glass Stays Misty
- Wipers Work Manually but Not in Automatic Mode
- Wipers Stop in the Wrong Position
- LED Bulb Upgrade Causes a Bulb Warning
- One Headlamp Flickers but the Other Is Stable
- Adaptive Headlight Warning After Front-End Repairs
- Brake Lights Stay On with the Pedal Released
- Number-Plate Lights and Rear Camera Fail Together
Vehicle networks and communication
- Scan Tool Connects to the Engine but Not the Body Systems
- A Module Communicates Until Its Motor or Actuator Runs
- Network Fault Appears After an Aftermarket Accessory Is Fitted
- Communication Fault Returns Only During Engine Starting
- Communication Fault Appears Only After the Vehicle Gets Hot
- CAN High and CAN Low: Why Wire Names Are Not a Diagnosis
- CAN FD Support: Why an Older Diagnostic Interface May Be Insufficient
- Automotive Ethernet Link Fault: Cable, Connection or Controller?
- A Diagnostic Topology Map Shows a Red Module: What Does That Prove?
- Several Historical Communication Codes After a Flat Battery
Programming, coding and module memory
- Same ECU Part Number: Is a Used Replacement Automatically Compatible?
- ECU Software Number and Hardware Number: Why Both Matter
- Interrupted ECU Update: What to Preserve Before Trying Again
- ECU Backup Files: Naming and Keeping the Original Read
- Module Checksum Error: Why Random File Correction Is Not a Repair Plan
- Coding Completed but a Replacement Feature Still Does Not Work
- Adaptation Refuses to Start: Check the Stated Preconditions
- Online Programming Account Error or Vehicle Programming Fault?
- EEPROM Replacement: Why a New Chip Is Not Automatically a Working ECU
- Replacement Module Has a Different VIN Stored
Engine control and electrical symptoms
- Engine Cuts Out When Hot but Restarts After Cooling
- Engine Cranks Normally but the Scan Tool Shows No Engine Speed
- Accelerator Pedal Responds Intermittently: Record Demand and Response
- Rough Running After an ECU Replacement
- Injector Circuit Fault Appears After Engine Repairs
- Engine Sensor Reading Jumps When the Harness Moves
- Cooling Fan Runs at Full Speed with a Cold Engine
- Engine ECU Reports Low Voltage but the Battery Tests Good
- Start-Stop Unavailable Without an Engine Warning
- Engine Warning Returns After a Sensor Has Been Replaced
Transmission control and gearbox symptoms
- Gear Selector Display Does Not Match the Lever Position
- Automatic Gearbox Engages Drive Only After a Delay
- Gearbox Warning Appears Only After a Long Journey
- Reverse Works but Forward Drive Does Not
- Gearbox Holds One Gear: What Limp Mode Does and Does Not Tell You
- Gearbox Judder Began After Adaptation Was Reset
- TCU Replacement: Why the Old Unit Should Stay with the Job
- Gearbox Controller Fault After Water Enters a Connector
- Gearbox Fault Appears When Selecting Park
- Transmission Solenoid Code: Electrical Test and Hydraulic Test Are Different
Driver assistance and cabin electronics
- Parking Sensors Sound Continuously with No Obstacle
- Rear Camera Picture Is Black but Parking Graphics Still Appear
- Surround-View Camera Images Do Not Line Up
- Driver-Assistance Warning After Windscreen Replacement
- Radar Warning After Bumper Repair
- Blind-Spot Monitoring Unavailable on One Side
- Lane Assistance Unavailable Without a Stored Engine Code
- Infotainment Has Sound but the Screen Is Blank
- Steering-Wheel Buttons Stop Working After Steering Work
- USB Socket Charges a Phone but Will Not Connect to the Car
Diagnostic evidence and repair verification
- Pending and Confirmed Fault Codes: Keep the Status with the Number
- Permanent Fault Code Remains After Repair: What to Ask Next
- Freeze-Frame Data and Live Data: Two Different Views of a Fault
- Readiness Monitors After Codes Have Been Cleared
- An Actuator Test Passes but the System Still Fails on the Road
- Scan Tool or Oscilloscope: Why a Workshop May Need Both
- Live-Data Logging Misses an Intermittent Fault: Improve the Capture
- Many Fault Codes at Once: Build a Timeline Before Replacing Modules
- Before Condemning an Engine ECU: Keep Mechanical Evidence in the Report
- After an Electrical Repair: What a Useful Verification Report Includes
More technical guides
Visit the automotive electronics repair library for fault-code explainers, module topics and other diagnostic resources. These educational guides support an enquiry; they do not replace vehicle-specific repair instructions or qualified assessment.